The present invention relates to a control system for industrial lift trucks and, more particularly, to a control arrangement in which a plurality of power functions may be controlled with a single manual control lever.
Various power lift trucks are known which are capable of performing a number of powered functions. Typically, such trucks are used in a material handling facility, are battery powered, and may include a provision for carrying the operator. Such trucks may also provide powered means for tilting the lift forks upward or downward, for clamping the forks together or spreading them apart, for shifting the forks together sideways, for extending the forks from the mast of the truck, as well as for raising and lowering the forks on the truck mast.
Some prior art truck designs have included separate controls for steering the truck and for each of the power functions. With such a control arrangement, it is necessary for the truck operator to move his hands between controls when changing from one power function to another. This is time consuming and inconvenient and requires that the operator direct his attention away from the material handling operation momentarily. Additionally, the operator might relinquish control of either the steering or velocity controls of the truck in order to manipulate the other controls. Obviously, this is not a desirable situation.
One approach taken to solve this problem is disclosed in U.S. Pat. No. 3,811,336 issued May 21, 1974, to Pulskamp, assigned to the assignee of the present invention. In the Pulskamp device, a control lever may be moved such that it pivots about a horizontal axis or about a vertical axis. When the lever is pivoted about the vertical axis, that is when it is moved generally horizontally, the position of the lever determines the speed of the lift truck. The lever is pivoted about the horizontal axis, that is, moved vertically, to control a second function, e.g. raising and lowering the forks. A switch is positioned on the end of the control lever in the Pulskamp device. When the switch is actuated, pivoting the lever about a horizontal axis controls a third function, such as tilting of the truck forks.
The Pulskamp disclosure suggests that a second button, positioned on the control lever, may be used for controlling the truck horn, or may, alternatively, be used to select another truck function for control by the control lever. It will be appreciated that there are a limited number of buttons that can be positioned on such a lever without impairing the operation of the control, since the operator will necessarily have to take care not to actuate the wrong button.
It is seen, therefore, that there is a need for a simple control system design in which a plurality of lift truck functions are selected for control by manipulation of a manual control and which design reduces the likelihood that the wrong function will be controlled.